This invention relates to waste treatment systems, and in particular, to a method for dose control of liquid treatment chemicals for the removal of nitrogen in wastewater streams.
The removal of nitrogen from wastewater streams is a two step process. In the first step the oxidation of ammonium to nitrate (nitrification) is accomplished by the aerobic growth of chemolithotrophic, autotrophic bacteria in an aerobic environment. The biochemical transformation is described by the following mass based stoichiometric equation, normalized to ammonium.NH4++3.30O2+6.708HCO3−0.129C5H7O2N+3.373NO3−+1.041H2O+6.463H2CO3 
In the second step, organic carbonaceous matter is oxidized by the growth of heterotrophic bacteria utilizing nitrate as the terminal electron accepter (i.e. denitrification). The equation describing the biochemical transformation depends on the organic carbon source utilized. The following is the mass based stoichiometric equation, normalized with respect to nitrate, with methanol as the organic carbon source.NO3−+0.324CH3OH0.226N2+0.591CO2+0.339H2O+0.274OH−
However, nitrification occurs only when the quantity of organic carbonaceous matter has been reduced according to the well-established criterion for the transition from oxidation of organics to nitrification, within the biofloc. The dichotomy of the process is that in order to achieve nitrogen removal a minimum carbon to nitrogen ratio (C/N) is required. Therefore, in order to achieve low levels of total nitrogen in the effluent, external sources of carbon may have to be added to a treatment process in order to remove the nitrates. Optimization of a chemical addition system can be achieved by an automated computer system with real time analysis of primary parameters effecting both denitrification and nitrification. Such a system would reduce the use of chemicals and avoid excess dosing.